The cytochrome P-450 mixed-function monooxygenase system (MFO) is involved in the metabolism of xenobiotics and carcinogens. Interferon (IFN) inducers and preparations decrease hepatic cytochrome P-450 levels and suppress the induction of the MFO system by 3-methylcholanthrene (3-MC) and phenobarbitol (PB). Some of the major objectives of this proposal are: 1) determine whether IFN inducer-dependent effects on the P-450 system are mediated by IFNs; 2) determine whether the various P-450 cytochromes are equally susceptible to IFN-dependent effects, and whether the different classes of IFNs (Alpha, Beta, Gamma) have differential effects on the P-450 cytochromes; 3) survey the effects of IFNs on P-450 mRNA synthesis; and 4) analyze the contribution of the IFN-dependent induction of xanthine oxidase (XO) to the modulation of the MFO system. Mice will be treated in vivo with IFN inducers or preparations (IFN-Alpha, Beta or Gamma) and the kinetics of overall P-450 loss and recovery will be determined in liver homogenates. Specific monooxygenase assays and immunoblot analyses of P-450 polypeptides separated on SDS acrylamide gels and probed with P-450 antibodies will be used to determine effects on specific P-450 species. Hybridization analyses with fragments complementary to specific 3-MC and PB inducible P-450 mRNAs will be used to determine IFN effects on P-450 mRNA transcription and processing. Allopurinol, an inhibitor of XO, will be used to determine whether the IFN-dependent induction of XO is responsible for modulating the MFO system. Since reactive oxygen species have been implicated in tumor promotion, the IFN-dependent induction of XO, which produces reactive oxygen species, suggests that IFNs might have "promoter-like" activities. The additional objectives of the proposal are: 5) to survey in murine skin and cultured keratinocytes the effects of IFNs on a variety of biochemical and morphological markers associated with the promotion stage of chemical carcinogenesis in murine skin; and 6) determine whether IFNs can coordinately moduclated enzymes (superoxide dismutase, catalase, and glutathione peroxidase) involved in the detoxification of reactive oxygen species. Allopurinol will be used in some studies to evaluate whether the IFN-dependent induction of XO is responsible for IFN "promoter-like" properties.